This invention relates to centrifugal separator apparatus for separating solid contaminants from a pumped liquid, by passage of contaminated liquid through a rotor from which it emerges as a jet that drives the rotor in rotation by reaction to the emerging liquid. The invention is particularly concerned with a rotor for such a self driven separator.
Such self-driven centrifugal separator apparatus is known from, for example, U.S. Pat. No. 4,787,975 (=EP 193,000), U.S. Pat. No. 6,224,531 (=WO 98/46361), U.S. Pat. No. 6,354,987 (=WO 99/54051), U.S. Pat. No. 6,457,868 (=WO 00/55515), U.S. Pat. No. 4,288,030 (=GB 2,049,494), GB 1,036,661, GB 710,510 and DE 10 93 617.
It is common for such separators to be used in cleaning particulates from lubricating oil circulated around an internal combustion engine. Such a separator then commonly comprises base structure that is mounted on the engine block to receive pumped oil at elevated pressure and return cleaned oil to the engine sump.
A cover supported on the base structure defines a housing enclosing a rotor that is free to rotate about an axis extending between the base structure and cover. For reasons known to those skilled in the art the rotation axis is desirably substantially vertical and the rotor is mounted via axially spaced bearings that permit contaminated liquid to enter the rotor substantially at the rotation axis and cleaned liquid to leave the rotor by tangentially directed reaction jet nozzle spaced from the rotation axis.
A considerable number of designs have been proposed to make such separators economical to manufacture and operate, whilst optimising, or at least not detracting from, efficient operation by comprising, rotation efficiency.
Insofar as successful operation results in the rotor filling with separated contaminants, it is necessary periodically to disassemble the housing, remove the rotor and replace it with an empty one, either by opening and cleaning the removed rotor or substituting it by a new one.
One of the approaches to achieving economy of operation is to have a throw-away rotor that requires no maintenance, providing that it can be made cheaply enough and rotate efficiently without requiring an expensive housing to compensate.
Rotor design is also influenced by, or influences, how it is mounted with respect to the housing and in this respect there are two major approaches, although each has variants.
An approach described in the aforementioned U.S. Pat. No. 4,787,975 involves having a solid axle or spindle fixed with respect to the housing and upon which both the rotor and housing cover are located, the axle also serving to direct oil to the rotor via drillings through the axle and provide journal surfaces against which rotor-borne bearing bushes slide. The pressure of supplied oil and/or thrust of the reaction jets may be used to apply weight countering force along the rotor axis and as such the sliding bearing bushes may include flanges to provide thrust bearings between the rotor and the base structure and/or cover.
A variant of this longitudinal fixed axle approach is described in GB 710,510 where a rotor is made of cheap materials and is supported in respect of thrust forces towards the cover by a ball making point contact with the rotor.
An alternative to having such a fixed elongate axle extending through the housing enclosure is to employ shorter stub axles either fixed to the housing or rotatable with the rotor.
U.S. Pat. No. 4,288,030 employs such stub axles formed at the housing structure and cover that co-operate with sliding bearing bushes in end of the rotor,
GB 1,036,661 and DE 1093617 each employ such stub axles that form parts of the spaced end walls of the rotor, at least one of the stub axles being hollow to permit entry of the contaminated liquid to the rotor, and lubrication of the bearings in which they slide by controlled leakage of the liquid they contain.
In keeping with having a separator and replacement rotor that is relatively cheap to manufacture, having such stub axles formed as part of the rotor is superficially attractive but such attraction may be lessened by compromises in rotation efficiency.
For example, if a rotor of the type shown in the aforementioned GB 1,036,661 or U.S. Pat. No. 4,288,030 is made from flimsy materials for economy, then the significant internal pressures developed during rotation tend to distort the rotor, including forcing the end walls apart, so that there is increased thrust loading on sliding bearings possibly to the point of jamming.
Rotor manufacture economy also points towards the molding of such rotor in two or more pieces to be joined as a self-contained rotor from synthetic resin (i.e., plastic) materials.
U.S. Pat. No. 6,224,531, U.S. Pat. No. 6,354,987 and U.S. Pat. No. 6,457,868 all disclose examples of centrifugal separators in which the rotors are molded from synthetic resin materials and assembled from few component parts.
The aforementioned U.S. Pat. No. 6,224,531 discloses constructions for a separator employing either a stationary spindle axle fixed to the base structure and stub axle shafts fixed to the rotor.
The aforementioned U.S. Pat. No. 6,354,987 and U.S. Pat. No. 6,457,868 also employ rotors made from molded synthetic resin components, but the rotor and walls have integrally molded stub axle shafts that engage with cooperating bearing parts in the housing base structure and cover. They address improved rotation efficiency by employing a ball race bearing in the cover, which offers low resistance to rotation whilst absorbing axial loads, and a sliding bearing in the base structure that includes a spherical element that effects alignment of the rotor with respect to the cover whilst obviating some of the need for precision of component manufacture.
However, molding such a rotor from synthetic resin materials requires sophisticated molding apparatus, and economy comes from manufacturing components in large numbers.
It will be appreciated that the rotor design disclosed in the aforementioned U.S. Pat. No. 4,787,975, although somewhat dated in terms of materials, may be made economically by less sophisticated methods, from relatively cheap thin sheet steel and the like, although not of course limited to any such material.